Insulation Part for Supporting an Electrically Conductive Nozzle in an Insulated Manner, and Laser Machining Head with a Sensor Assembly for Detecting such an Insulation Part

ABSTRACT

The invention relates to an insulation part for supporting an electrically conductive nozzle in an insulated manner, and a laser machining head with a housing ( 10 ), through which a working laser beam path ( 11 ) is guided, which exits on the machining side through an electrically conductive nozzle ( 17 ), which is supported on an insulation part ( 18 ), which is supported on the housing ( 10 ), and which, for the capacitive distance measurement, is electrically connected to an oscillating circuit ( 24 ) of a distance measuring circuit ( 22 ). To be able to monitor the presence of an inexpensive insulation part ( 18 ) in a user-friendly manner, it is provided according to the invention that the insulation part ( 18 ) comprises a ferromagnetic body ( 26 ) and that a sensor ( 27 ) for detecting the ferromagnetic body ( 26 ) is provided on the housing ( 10 ), said sensor being connected to a monitoring circuit ( 29 ), which, in the absence of an insulation part ( 18 ), outputs a warning signal.

The invention relates to an insulation part for supporting anelectrically conductive nozzle, in particular a cutting nozzle tip, inan insulated manner on a laser machining head as well as a lasermachining head provided therewith, in particular a laser machining headwith integrated capacitive distance regulation.

To be able to reach optimal machining quality and the highest machiningspeed in response to the laser machining, it is required that thedistance between workpiece and laser machining head, in particular thedistance between cutting nozzle and workpiece, are kept constant,because the smallest deviations already diminish the machining quality.Deviations from the target distance lead to burr formation orunfavorably impact the cutting speed, the roughness depth of the cuttingsurfaces and the gap width, in particular in response to the lasercutting. Laser machining heads, in particular laser cuttings heads, arethus equipped with a capacitive distance measuring system forcapacitively measuring the distance between workpiece and cuttingnozzle. The distance measuring system has a conductive cutting nozzletip, as sensor electrode, which, with the workpiece, forms the measuringcapacitor, which is integrated into an oscillating circuit. To fastenthe conductive cutting nozzle tip to the nozzle body of the lasermachining head, parts are frequently used, which do not only serve thepurpose of supporting the conductive nozzle tip, but also for theelectric insulation thereof against the nozzle body and the housing.

Insulation parts of a known design are often made of ceramic material,aluminum with insulating coating or with an insulation by plastic rings.

If the user forgets to insert this insulation part and starts thedistance regulation, the laser machining head is moved against theworkpiece and collides with it, because the nozzle tip is then connectedto ground, as is the workpiece, so that a capacitor between nozzle tipand workpiece cannot be formed.

A method, in which it can be detected when the insulation part ismissing, by monitoring the internal capacitance of the nozzle assembly,is known from DE 101 21 655 C1. A collision of the laser machining headwith the workpiece can then be prevented by means of a correspondingsignal processing. This method requires, however, that the nozzlesupport forms an internal capacitance with the conductive nozzle tip andcan thus be monitored for the presence of an insulation.

In the case of capacitance measuring devices for the distanceregulation, which work according to the principle of the activeshielding, the internal capacitance is eliminated by means of themeasuring method and can thus not be used for the monitoring.

A method for capacitively measuring the distance between a sensorelectrode and a workpiece is known from DE 199 06 442 A1, in the case ofwhich the measuring line to the sensor electrode is actively shielded,wherein the measuring voltage tapped via the measuring line is appliedto the shielding of the measuring line via an impedance converter.Internal or parasitic capacitances, which are parallel to the measuringcapacitance, can be reduced significantly in this way. However, theinternal or parasitic capacitances are thus also not available formonitoring the presence or absence of an insulation part.

It is known from DE 42 01 640 C1 to provide two lines in an insulationpart, which are connected to one another via the conductive nozzle tip.An interruption of this connection can be evaluated to determine whetheror not the insulation part is present or whether the sensor element isabsent. This solution, however, is mechanically highly complex and thuscreates costs, which are disproportionately high for a wear part.

An insulator of a two-piece construction for the insulated support of anelectrically conductive nozzle on a laser machining head, which consistsof an insulation part for the electrical insulation, and of a shieldingpart for shielding against radiation and/or heat, and which has acentral through opening for a working laser beam is known from EP 1 977193 B1. The two-piece embodiment of the insulator makes it possible toprovide an insulator, which is simpler in terms of production and thusinexpensive, for a laser machining head. The shielding part serves thepurpose of shielding against laser radiation reflected back from aworkpiece and consists of a non-conductive material, which is resistantto heat.

EP 2 444 183 A1 describes an insulating section of a laser machininghead for supporting an electrically conductive nozzle. The insulatingsection comprises an outer insulation part and an inner insulation part,which are arranged coaxially to one another and have a central throughopening for a working laser beam. An accommodation for a sensor part,which forms a type of metal interface between a contact pin in theinsulating section and the electrically conductive nozzle, is providedin the through opening of the outer insulation part. The innerinsulation part can be embodied as simple metal sleeve and can consistof brass, aluminum, copper or stainless steel. With the first insulationpart, the insulating section makes it possible to provide an electricalinsulation and, with the second insulation part, to shield the firstinsulation part against thermal impacts from the working laser beam.

The invention is thus based on the object of providing an insulationpart for supporting a nozzle tip on a laser machining head, theproduction of which is inexpensive and the absence or presence of whichon a laser machining head can be monitored in a user-friendly manner.The invention is further based on the object of creating a lasermachining head, which is suitable for a user-friendly monitoring of theabsence or presence of the insulation part.

These objects are solved by means of the insulation part according toclaim 1 or the laser machining head according to claim 6, respectively.

According to the invention, an insulation part, which supports anelectrically conductive nozzle on a housing of a laser machining head inan insulated manner with respect thereto, thus comprises a piece of aferromagnetic material, the presence of which can be detected by meansof a sensor. This embodiment of the insulation part does not onlyprovide for an inexpensive production of the insulation part, but also auser-friendly monitoring of the presence of the insulation part, so thatthe risk of damages to a laser machining head due to a faulty distanceregulation can be ruled out securely.

It is provided in the case of an advantageous embodiment of theinvention that the electrically insulating body is a ceramic body, inwhich the ferromagnetic body is embedded. Due to this embodiment of theinsulation part, the latter can be produced particularly inexpensively,because, except for the embedding of the ferromagnetic body, theproduction can take place in the same way as in the case of commoninsulation parts.

It is provided in a different embodiment of the invention that theinsulation part comprises a ring-shaped ferromagnetic body, which isembedded in an electrically insulating coating made of plastic.

Instead of the use of a ferromagnetic material, such as iron, forexample, it is also possible according to a further development of theinvention to use an alloy with a low Curie temperature, in particular anickel/cobalt/iron-based alloy. In the case of temperatures below theCurie temperature, the presence of the insulation part can be detectedby means of such a ferromagnetic body. If the temperature of the lasermachining head and thus the temperature of the ferromagnetic body risesabove the Curie temperature thereof, the body can no longer be sensed bya sensor, which then outputs a corresponding warning signal to a machinecontroller. Not only the presence of an insulation of the conductivenozzle can thus be monitored in a simple manner, but the laser machininghead can be protected against overheating as well.

An advantageous embodiment of the invention is characterized in that asensor for detecting the ferromagnetic body of the insulation part isprovided on a housing of a laser machining head, on which anelectrically conductive nozzle of a distance measuring circuit issupported by means of an insulation part according to the invention,said sensor being connected to a monitoring circuit, which outputs awarning signal in the absence of an insulation part.

The invention will be described in more detail below, for example bymeans of the drawing, where:

FIG. 1 shows a schematic, simplified sectional view of a laser machininghead, and

FIG. 2 shows a schematic, simplified sectional view of a furtherinsulation part for a laser machining head.

Components, which correspond to one another, are provided with identicalreference numerals in the different figures of the drawing.

As illustrated in FIG. 1, a laser machining head has a housing 10,through which a working laser beam path 11 is guided, in which a lensassembly 12 for focusing a working laser beam 14 to a workpiece 15 isprovided. A nozzle head 16, on which an electrically insulating nozzle17 is provided, which is electrically insulated against the nozzle body16 by an insulation part 18, is attached to the machining-side end ofthe housing 10. The insulation part 18 is fastened to the nozzle body16, for example by means of a cap nut 19. As can be seen particularlywell in FIG. 2, the insulation part 18, 18′ has a central throughopening 20, which, on its machining-side end, is provided with aninternal thread 20′, is screwed into the electrically conductive nozzle17 with a corresponding counter thread 21.

The electrically conductive nozzle 17, which consists of copper, forexample, is electrically connected to an oscillating circuit 24 of acapacitive distance measuring circuit 22, as is schematically suggestedby the dashed line 23. The electrically conductive nozzle 17, togetherwith the workpiece 15, forms a capacitor, which is integrated into theoscillating circuit 24 of the capacitive distance measuring circuit 22,and the capacitance of which changes with the distance between lasermachining head and workpiece 15, thus with the distance betweenelectrically conductive nozzle 17 and workpiece 15. The capacitivedistance measurement is known to the person of skill in the art and isdescribed, for example, in the prior art publications mentioned above.The distance measurement thus does not need to be described in moredetail.

According to a first exemplary embodiment of the invention, theinsulation part 18 has a ring-shaped ceramic body 25, in which aferromagnetic body 26 is embedded. A sensor 27 for detecting theferromagnetic body 26, is arranged in the nozzle body 16, locatedopposite to the ferromagnetic body 26. The sensor 27 is connected via aline 28 to a monitoring circuit 29, which, in the absence of aninsulation part 18, outputs a warning signal to a machine controller,which is not illustrated, and thus blocks the distance regulation.

In the alternative, the insulation part 18′ can also have aferromagnetic body 36, which essentially has the shape of thering-shaped ceramic body 25, and which is embedded in a plastic coatingor sheathing 37. Instead of the insulating coating, plastic rings canalso be provided in a manner, which is not illustrated in more detail,which realize the required insulation of the electrically conductivenozzle 17 against the nozzle body 16 and the housing 10 of the lasermachining head.

Instead of a ferromagnetic material, such as iron, for example, an alloywith low Curie temperature, in particular a nickel/cobalt/iron(NiCoFe)-based alloy, can be provided as well. Such NiCoFe-based alloyswith further metallic and non-metallic additives, which areferromagnetic blow their Curie temperature, but which lose theirferromagnetic property when exceeding the Curie temperature, are knownin the prior art. Due to this property, it is then possible to protectthe laser machining head against overheating, with suitably selectedalloy with matching Curie temperature, because the ferromagnetic body26, 36 can no longer be detected when exceeding the Curie temperature,so that the monitoring circuit 29 outputs a corresponding warning signalto the machine controller, which then interrupts the ongoing machiningof a workpiece.

According to the invention, the presence of the insulation part 18between electrically conductive nozzle 17 and nozzle body 16 or housing10 can thus be monitored in a simple manner by detecting theferromagnetic body 26, 36, which is embedded in the insulation part, sothat a collision between laser machining head and workpiece due to afaulty capacitive distance measurement cannot be ruled out reliably.

1. An insulation part for supporting an electrically conductive nozzlein an insulated manner on a laser machining head, with a ring-shapedelectrically insulating body, which has a central through opening for aworking laser beam path, as well as first means set up for supportingthe insulation part on the laser machining head, and second means set upfor supporting an electrically conductive nozzle, characterized in thatthe electrically conductive nozzle has a ferromagnetic body.
 2. Theinsulation part according to claim 1, characterized in that theelectrically insulating body is a ceramic body, in which theferromagnetic body is embedded.
 3. An insulation part for supporting anelectrically conductive nozzle in an insulated manner on a lasermachining head, characterized in that it has a ring-shaped ferromagneticbody with a central through opening for a working laser beam path, aswell as with first means set up for supporting the insulation part onthe laser machining head and second means set up for supporting anelectrically conductive nozzle, which is embedded in electricallyinsulating plastic.
 4. The insulation part according to claim 3,characterized in that the ferromagnetic body consists of an alloy with aCurie temperature, which is so low that a laser machining head withattached insulation part can be protected against overheating.
 5. Theinsulation part according to claim 4, characterized in that the alloywith low Curie temperature is a nickel/cobalt/iron (NiCoFe)-based alloy.6. A laser machining head with a housing, through which a working laserbeam path is guided, which exits on the machining side through anelectrically conductive nozzle, which is supported on an insulationpart, which is supported on the housing and which, for capacitivedistance measurement, is electrically connected to an oscillatingcircuit of a distance measuring circuit, wherein a sensor for detectingferromagnetic body of the insulation part is provided on the housing,said sensor being connected to a monitoring circuit, which, in theabsence of an insulation part, outputs a warning signal, wherein theinsulation part has a central through opening for a working laser beampath, as well as first means set up for supporting the insulation parton the laser machining head, and second means set up for supporting anelectrically conductive nozzle, characterized in that the electricallyconductive nozzle has the ferromagnetic body.